Tissue engineering is a field in which the principles of biology, engineering, and materials science are applied to the development of functional substitutes for damaged tissue. (See, Langer, et al., xe2x80x9cTissue Engineeringxe2x80x9d, Science, 1993, 260, 920). In general, three different strategies have been adopted for the creation of new tissue: (i) isolated cells or cell substrates, in which only those cells that supply the needed function are replaced; (ii) tissue-inducing substances, such as signal molecules and growth factors, and (iii) cells placed on or within matrices. Researchers have been interested in applying these novel techniques to find replacements for tissues such as ectodermal, endodermal, and mesodermal-derived tissue. In particular, researchers are invested the replacement of tissues in the nervous system, cornea, skin, liver, pancreas, cartilage, bone, and muscle to name a few.
Stem cells have shown tremendous potential for treatment of diseased and damaged tissue. Stem cells are cells that have the potential to both divide for indefinite periods in vitro and to differentiate into more specialized cells. Pluripotent stem cells are a potential source for the development of replacement tissues to treat a variety of medical conditions. For example, nerve stem cells transplanted into the brain may develop into healthy nerves that can counteract the affect of Alzheimer or Parkinson""s disease. Tissue engineering applications have long exploited fully differentiated cells seeded onto biocompatible matrices that may be implanted in a wound site to regenerate damaged tissue. The incorporation of stem cells into tissue engineering matrices may increase the therapeutic potential of this technique.
Typically, tissue engineering matrices are designed to either replicate or facilitate restoration of the structural properties of the damaged tissue. The use of electroactive polymers in tissue engineering matrices allows these matrices to replicate or restore the electrical properties of tissue as well. For example, bone is piezoelectric and generates an electrical voltage when mechanically deformed. The electrical activity may mediate remodelling of bone in response to mechanical loading (FIG. 1) (Fukada et al., J. Phys. Soc. Japan, 1957, 12, 1158; Becker et al., xe2x80x9cThe Bioelectric Factors of Controlling Bone Structurexe2x80x9d, in Bone Biodynamics, R. Bourne, Ed., 1964, Little, Brown and Co.: New York; Bassett et al., Nature, 1964, 204, 652). Nerve cells of course work by transmitting electrical signals from the brain to various muscles, and other tissues are responsive to electrical stimulation as well.
Clearly, there remains a need to develop systems and methods whereby biological activities of cells can be stimulated by direct application of electromagnetic stimulation. This would be particularly important in applications to tissue engineering.
The concept of xe2x80x9ctissue engineeringxe2x80x9d comes into play in the present invention for the development a system in which the biological activities of cells can be stimulated. An interesting class of synthetic polymers explored previously by Langer and co-workers as three-dimensional matrices that can take advantage of these properties are the electrically conducting or electroactive polymers. Based on their ability to respond to electrical or electromagnetic stimuli, they can act as an interface between the external and physiological environments of a connective tissue such as bone, which is capable of undergoing repair and regeneration on exposure to the same stimuli (Shastri et al., xe2x80x9cBiomedical Applications of Electroactive Polymersxe2x80x9d, in Electrical and Optical Polymer Systems, D. L. Wise, Wnek, G. E., Trantolo, D. J., Cooper, T. M., Gresser, J. D., Ed., 1998 Marcel Dekker: New York, 1031).
The present invention provides compositions, methods and systems for the stimulation of biological activities within cells by applying electromagnetic stimulation to an electroactive material, wherein the electromagnetic stimulation is coupled to the electroactive material. The present invention provides methods for the stimulation of biological activities within stem cells that involve attaching or associating the stem cells to or with a surface comprising an electroactive material, and applying electromagnetic stimulation directly to the desired area. In preferred embodiments, the stimulation of biological activities within these cells results from inducing one or more activities including, but not limited to, gene expression, cell growth, cell differentiation, signal transduction, membrane permeability, cell division, contraction, and cell signaling. In exemplary embodiments, the electroactive materials are either two-dimensional substrates or three-dimensional substrates comprising a matrix having at least one surface of an electroactive material.
In another aspect, the invention is a method for stimulating one or more biological activities within a cell comprising a composition of stem cells and an electroactive substrate, wherein the electroactive substrateic has at least one surface of electroactive material and the stem cells are attached to the electroactive material or associated with the electroactive substrate. Electromagnetic stimulation coupled to the electroactive material is applied to the composition. The composition is contacted with a mammalian tissue either before or after the step as applying.
In another embodiment, a composition of cells and an electroactive substrate is first provided, wherein the electroactive substrate has at least one surface of electroactive material, and wherein the cells are attached thereto or associated with the electroactive substrate. Subsequently, the electromagnetic stimulation is applied to the composition in vitro, wherein the electromagnetic stimulation is coupled to the electromagnetic material and finally the composition is contacted with mammalian tissue to effect stimulation of cell function. In yet another embodiment, a composition of cells and an electroactive substrate is first provided, wherein the cells are attached thereto or associated with the electroactive substrate. Subsequently, the composition is then contacted with mammalian tissue, and finally the electromagnetic radiation is applied in vivo, wherein the electromagnetic stimulation is coupled to the electroactive material. In particularly preferred embodiments, the electromagnetic stimulation is coupled to the electroactive material by physical contact. In other embodiments, the electromagnetic stimulation is coupled to the electroactive material by electromagnetic induction.
In another aspect of the invention, a system is provided for stimulating one or more biological activities of cells comprising a composition comprising an electroactive substrate, wherein the electroactive substrate has at least one surface of electroactive material, and wherein the electroactive material has attached thereto, or associated therewith, one or more mammalian stem cells. The system further includes apparatus for applying electromagnetic energy at the desired location.
Yet another aspect of the present invention is a two-dimensional stimulant of one or more biological activities of cells comprising one or more films of an electroactive substrate, wherein the one or more films are associated with or attached to one or more mammalian cells at a desired location. A three-dimensional stimulant of one or more biological activities of cells is also provided comprising an electroactive substrate associated with or attached to a matrix and wherein the electroactive substrate is associated with or attached to one or more mammalian cells at a desired location.
xe2x80x9cElectromagnetic Stimulationxe2x80x9d: As used herein, the term xe2x80x9celectromagnetic stimulationxe2x80x9d means any form of electromagnetic energy including, but not limited to, electromagnetic radiation or pulsed electromagnetic field stimulation (PEMF).
xe2x80x9cElectroactive materialxe2x80x9d: As used herein, the term xe2x80x9celectroactive materialxe2x80x9d means a material that contains pockets of electron density. This material may be conducting, non-conducting, semiconducting, or piezoelectric, to name a few. For the purposes of the present invention, preferred electroactive materials include electroactive polymers. These electroactive polymers are characterized in that they contain at least a pocket of electron density and are capable of undergoing a phase transition upon subjecting the polymer to an electromagnetic field stimulus.